A wide variety of devices and techniques have been developed to diagnose and treat vascular diseases. Coronary artery disease (CAD) is a vascular disease in which blood flow to the heart muscle is restricted by abnormal deposits in the coronary arteries. The abnormal deposits deprive portions of the heart muscle of essential oxygenated blood. The wide spread impact of coronary artery disease has stimulated the development of diverse types of therapeutic and diagnostic devices.
Percutaneous transluminal coronary angioplasty (PTCA) has gained wide acceptance as an effective and minimally invasive method of treating coronary artery disease. A typical PTCA procedure involves the use of an angioplasty balloon catheter. Examples of over-the-wire type balloon catheters are described in commonly assigned U.S. Pat. No. 4,976,690 to Solar, and U.S. Pat. No. 5,047,045 to Arney. The balloon catheter is inserted into the body by way of the femoral artery and is navigated to a coronary artery, assisted by a guide catheter and a guide wire. The balloon is positioned across a restriction in the artery and the balloon is subsequently inflated. The inflated balloon compresses the restriction outwardly, thus opening the restriction and restoring blood flow to portions of the heart muscle previously deprived of oxygenated blood.
Other minimally invasive techniques have been developed as alternatives to balloon PTCA. For example, atherectomy devices are designed to treat specific types of lesion morphology. Atherectomy, as distinguished from balloon PTCA, removes the abnormal deposit or lesion from the vessel rather than molding or compressing the restriction with a balloon.
Other medical devices have been developed for use in combination with balloon PTCA. Balloon expandable stents, for example, are used post-PTCA to prevent a dilated restriction from re-closing. A balloon-expandable stent is delivered to the location of the dilated restriction using a balloon catheter. The stent is mounted in its collapsed position onto a deflated balloon and the balloon catheter is navigated through the vasculature to the portion of the vessel previously dilated. The balloon is expanded to open the stent causing it to engage the inner wall of the vessel. The balloon is then deflated and the balloon catheter is removed, leaving the stent securely in place across the dilated restriction.
PTCA balloon catheters, atherectomy devices, stents as well as several other intravascular devices require some means to visualize the operation of the devices while inside the body. The most common method of visualization is angiography. Angiography involves the injection of radiopaque contrast fluid into the vessel while simultaneously viewing the subject vessel radiographically. Angiography is limited to viewing the subject vessel in a monochromatic two-dimensional plane with no depth of field. To partially compensate for this limitation, a plurality of planar views can be taken and a three dimensional view can be mentally assimilated. However, this method inherently involves a certain amount of human error and since each view must be taken in sequence, critical time is wasted which may jeopardize the health of the patient. In addition, since angiography is limited to monochromatic views, it is not able to accurately identify the pathology of abnormal deposits within the vessel.
Angioscopes, by contrast, allow the treating physician to view a vessel in a polychromatic two dimensional plane with depth of field. The ability to view in two dimensions with depth of field allows the physician to ascertain the morphology of the vessel and the obstructive material in a more accurate and timely manner. Furthermore, the ability to view in color allows the physician to identify the pathology of the obstructive material (e.g. thrombus, plaque and the like). By utilizing angioscopy, the physician can modify the therapy as a function of the pathology and morphology of the obstructive material in the vessel.
Intravascular angioscopy requires a means to displace optically opaque blood from the field of view. The most common method of displacing opaque fluid utilizes an occluding balloon to block the flow of blood proximal to the portion of the vessel to be viewed. An optically transparent fluid such as saline is then flushed distal of the occluding balloon and the angioscope can then view through the optically transparent fluid. However, utilizing an occluding balloon deprives portions of the heart of essential oxygenated blood and often results in ischemia and patient discomfort. As such, this method is limited to short intervals typically 30 to 45 seconds. Also, the profile of such occluding balloon catheters is large because the catheter must provide a large flush lumen in addition to an inflation lumen, a guide wire lumen and an angioscope lumen. It is desirable to minimize the profile for intravascular applications. In addition, some of the prior art devices that utilize this method include integral angioscopes which are not removable and thus inherently increases the cost of the device.
Another method of displacing optically opaque fluid from the field of view utilizes a fluid displacing balloon. In this method, a balloon is inflated with an optically transparent fluid such as saline and is thereby expanded to come into contact with the interior of the vessel. The angioscope can then view through the optically transparent fluid. However, the prior art devices that utilize this method include integral angioscopes which are not removable and thus inherently increase the cost of the device. Also, the profile of such occluding balloon catheters is large because the catheter must provide an angioscope lumen in addition to an inflation lumen and a guide wire lumen. Again, it is desirable to minimize the profile of intravascular devices in order to have access to small diameter vessels.
In addition, prior art intravascular angioscopes do not provide a means to collect quantitative information about the vessel and obstructions within the vessel. Angiography, by contrast, provides some quantitative information but is limited to measuring dimensions in only one plane. As such, it is desirable to retain all the benefits of angioscopy and provide a means to gain quantitative information.
Examples of intravascular angioscopes include the device disclosed in U.S. Pat. No. 4,470,407 to Hussein. Hussein '407 discloses an endoscopic device including an elongated tube carrying an expandable balloon on its distal end which displaces opaque fluid such as blood and allows for viewing of the walls of the duct which come into contact with the balloon. In addition, U.S. Pat. No. 5,090,959 to Samson et al. discloses an imaging balloon dilation catheter for use in angioplasty. Further, U.S. Pat. No. 5,116,317 to Carson Jr., et al. discloses a balloon-type catheter with an integral optical system for use in angioplasty.
In general, it is desirable to have an over-the-wire type dilating balloon catheter for use in combination with an angioscope. In particular, it is desirable to be able to manipulate and navigate such a balloon catheter independent of the angioscope. It is also desirable to be able to exchange a first balloon catheter for a second balloon catheter without wasting the integral angioscope of the first balloon catheter. Additionally, it is desirable to have quick and easy access to the treatment site with the angioscope when the catheter is already in place. It is further desirable to visualize different areas of the treatment site while the therapy is in progress and to have the ability to quantitatively assess dimensional aspects of the objects being viewed.
Thus, there is a need for a device which satisfies these desirable aspects and overcomes the associated disadvantages of the prior art. The present invention overcomes the disadvantages of the prior art and additionally provides several inventive features that can be fully appreciated by a review of the following summary and detailed description.